package com.ymy.boot.aqs;

import org.jetbrains.annotations.NotNull;

import java.io.Serializable;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * @author Ringo
 * @date 2021/10/19 14:19
 */
public class AQSNonReentrantLock implements Lock, Serializable {

    /**
     * 内部帮助类
     */
    private static class Sync extends AbstractQueuedSynchronizer {
        /**
         * 判断是否处于锁定状态
         * <p>
         * - 1: locked
         * - 0: unlocked
         */
        @Override
        protected boolean isHeldExclusively() {
            return getState() == 1;
        }

        /**
         * 如果 state = 0 就尝试获取锁
         * <p>
         * 将 state 设置为 1
         */
        @Override
        protected boolean tryAcquire(int acquires) {
            // assert acquires == 1;
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }

        /**
         * 释放锁
         * <p>
         * 将 state 设置为 0
         */
        @Override
        protected boolean tryRelease(int releases) {
            if (getState() == 0) {
                throw new IllegalMonitorStateException();
            }
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }

        Condition newCondition() {
            return new ConditionObject();
        }
    }

    private final Sync sync = new Sync();

    @Override
    public void lock() {
        sync.acquire(1);
    }

    @Override
    public boolean tryLock() {
        return sync.tryAcquire(1);
    }

    @Override
    public void unlock() {
        sync.release(1);
    }

    public boolean isLocked() {
        return sync.isHeldExclusively();
    }

    public boolean hasQueuedThreads() {
        return sync.hasQueuedThreads();
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }


    @Override
    public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireNanos(1, unit.toNanos(timeout));
    }


    @NotNull
    @Override
    public Condition newCondition() {
        return sync.newCondition();
    }
}
